Climate Change Causes River Network Contraction and Disconnection in the H.J. Andrews Experimental Forest, Oregon, USA

Abstract

Headwater streams account for more than 89% of global river networks and provide numerous ecosystem services that benefit downstream ecosystems and human water uses. It has been established that changes in climate have shifted the timing and magnitude of observed precipitation, which, at specific gages, have been directly linked to long-term reductions in large river discharge. However, climate impacts on ungaged headwater streams, where ecosystem function is tightly coupled to flow permanence along the river corridor, remain unknown due to the lack of data sets and ability to model and predict flow permanence. We analyzed a network of 10 gages with 38-69 years of records across a 5th-order river basin in the U.S. Pacific Northwest, finding increasing frequency of lower low-flow conditions across the basin. Next, we simulated river network expansion and contraction for a 65-year period of record, revealing 24% and 9% declines in flowing and contiguous network length, respectively, during the driest months of the year. This study is the first to mechanistically simulate network expansion and contraction at the scale of a large river basin, informing if and how climate change is altering connectivity along river networks. While the heuristic model presented here yields basin-specific conclusions, this approach is generalizable and transferable to the study of other large river basins. Finally, we interpret our model results in the context of regulations based on flow permanence, demonstrating the complications of static regulatory definitions in the face of non-stationary climate.

Using isotopes to understand landscape‐scale connectivity in a groundwater‐dominated, lowland catchment under drought conditions

“…on spatial dynamics of surface water availability, stream connectivity and modification of the seasonal tracer signal (e.g., YWF) in such lowland landscapes. Catchment‐specific patterns of river network disconnection are becoming more widely investigated in contrasting environments and have been related to climate change‐induced water balance alterations, very localized site characteristics (e.g., in the steep, forested Pacific Northwest; Ward et al, 2020), and landscape structure (Bertrand et al, 2012). More explicit, an assessment of the role of land use and vegetation age classes (Germer et al, 2011) on groundwater recharge and spatial connectivity patterns could be usefully integrated into further analysis through spatially distributed hydrological modelling (Holman et al, 2017).…”

Analysing river network dynamics and active length - discharge relationship using water presence sensors

“…important ecosystems services, among which the transport of material or organisms that support the biodiversity of downstream ecosystems (Datry et al, 2014;Leigh et al, 2016;Stubbington et al, 2017;Acuna and Tockner, 2010). The development of specific laws governing the use of water in non-permanent streams would represent an important step forward in water policy, since the number and extension of temporary streams is likely to increase in the future due to the combined action of urbanization, ground and surface water withdrawal and climate change (Creed et al, 2017;Jaeger et al, 2019;Ward et al, 2020). To raise awareness of the importance of temporary streams in the scientific community and the society, it is fundamental to provide the community with new data about network expansion and contraction, possibly exploiting recent technological advancements in instrumentation and models (Acuna et al, 2014;Whol, 2017).…”

Intermittent rivers and ephemeral streams: Perspectives for critical zone science and research on socio‐ecosystems

“…Major challenges remain for developing a holistic understanding of IRES. Low regional synchronization of zero flows reveals unknown processes that control intermittence (Snelder et al, 2013), especially the relative influence of natural drivers like climate (Borg Galea et al, 2019; Skoulikidis et al, 2017; Ward, Wondzell, Schmadel, & Herzog, 2020), geology (Lovill et al, 2018; Ward et al, 2018; Whiting & Godsey, 2016), topography (Jensen et al, 2018; Jensen et al, 2019; Prancevic & Kirchner, 2019), and of human factors such as land use and water withdrawals (de Graaf et al, 2019; Dresel et al, 2018; Skoulikidis et al, 2017). It is also unclear how drying alters the estimation of water balance (Cuthbert et al, 2016) and water travel times (Bansah & Ali, 2019; van Meerveld, Kirchner, Vis, Assendelft, & Seibert, 2019).…”